Magnetic memories, in particular magnetic random access memories (MRAMs), are attracting attention due to their potential for high-speed read operation, high-speed write operation, superior durability, nonvolatile property, and low power consumption during operation. The MRAMs are nonvolatile memories that operate based on the giant magneto resistive effect (GMR) or the tunnel magneto resistance effect (TMR), and store data using a magnetic material as a medium for recording and retaining data. Magnetic members included in memory devices are being miniaturized in order to increase the memory density. As the magnetic members are miniaturized, the magnetic field used in an operation of the memories needs to be applied to the minute magnetic members. However, it is difficult to locally generate a magnetic field since the magnetic field tends to spread to the space. If the size of the magnetic field source is deceased to form a local magnetic field, the size of the local magnetic field may not be satisfactory to control the direction of the magnetization of the magnetic material.
In order to solve this problem of the MRAMs, such memories are known as spin transfer torque magnetic random access memories (STT-MRAMs), in which the direction of magnetization of a magnetic member is switched by causing a current to flow through the magnetic member, spin-hall effect magnetic random access memories (SHE-MRAMs), in which the direction of magnetization is switched by causing a current to flow through a nonmagnetic heavy metal that provides a great spin Hall effect, voltage-control magnetic random access memories (VC-MRAMs), in which a write operation is performed by using a voltage control magnetic anisotropy effect, and the number of electrons in the magnetic member is changed by applying a voltage to a magnetic tunnel junction (MTJ), thereby changing the magnetization characteristics, and voltage-control spintronics memories (VoCSMs) using the spintronics technology, in which SHE-MRAMs are arranged in a string structure and the VCMA effect is used to select the bit on which a write operation is performed. The above methods are expected to locally control the magnetization state in the nano-scale magnetic member, and to reduce the value of the current for switching the magnetization as the size of the magnetic material is reduced.
In the STT-MRAM method, the same terminals are used for a write operation and a read operation, and a large current is used for the write operation and a small current is used for the read operation to prevent the magnetization switching (writing) caused by the read current.
In the SHE-MRAMs, terminals for a write current may be separated from terminals for a read current. Therefore, these memories are expected to reduce the write error rate (WER).
The VoCSMs have a string structure in which SHE-MRAMs having three terminals and a large cell size are connected. Therefore, these memories are expected to be highly integrated. As memory elements are miniaturized and highly integrated, the influence of the leakage magnetic field from the storage layer on adjacent memory elements increases, which increases the write error rate. Therefore, the storage layer needs to have a synthetic anti-ferromagnetic (SAF) structure which generates less leakage magnetic field and thus may suppress the increase in write error rate caused by the leakage magnetic field. It is known that if the storage layer is sandwiched by conductive layers with opposite spin Hall angles, and a current is caused to flow these conductive layers, the magnetization switching efficiency is improved by the spin Hall effect. The improve in magnetization switching efficiency leads to a decrease in write current, and therefore a decrease in power consumption. However, it has been difficult to cause a current to flow through the layers on and under the storage layer.